Serial

3G modem

OEM Firmware

The most recent version of the OEM firmware is not the 301b1 or 300b7 but the 301b7. It can be found on the D-Link DWR-921 support page.

FW installation

The DWR-921 is shipped with the JBOOT bootloader.
Two option are theoretically possible to install the openwrt/lede fw

Prepare a factory image and load the squashfs-factory.bin from the jboot bootloader.

Replace the JBOOT with the UBOOT bootloader and install the squashfs-sysupgrade.bin firmware directly from uboot.

The first option is for sure the less risky, but currently is unsupported. Therefore the only supported option, is replace the uboot using flashrom with a proper flash adapter/interface. It shall be higlihted that with this operation you can easly brick your router if you don't know what you are doing.

Everybody agree that the best way to support this device in LEDE is to generate a FOSS utility able to preapre the properly formatted image accepted by the stock jboot bootloader. In order to prepare this utility it is required to decode the factory image. This task is not easy, therefore the help from everybody is appreciated. The details about what currently realized about the dwr-921 factory format image are reported here: DWR-921 Stock Image Cracking